Market penetration of wide band gap devices tends to promote low-inductance Surface Mounted Device (SMD) packages where heat extraction is realized through the Printed Circuit Board (PCB). It also tends to promote new packaging technologies where the power semiconductor dies are embedded within the PCB. These two trends allow not only fast switching cell, but also low-cost assembly.
The thermal resistance of the PCB can be sufficiently reduced with thermal vias or thick metal inlays. The main bottleneck is presently on the thermal interface between PCB and heat-sink, that requires: a high conformability to compensate the large irregularities of the PCB and for bending effects due to unequal pressure application and thermo-mechanical strain, a high thermal conductivity to improve the cooling efficiency, an electric isolation between heat-sink and the PCB for security reasons, and finally low material and process costs.
Most thermal interface solutions commercially available today exhibit either low conformability and/or low thermal conductivity like for example FR4 pre-preg, polymide and/or no/low electric isolation like for example thermal grease, graphite pads, and/or high cost like for example isolating pads.
One reason is that present thermal interface materials are designed to provide an interface with a homogeneous and high thermal conduction on the entire surface. This feature is not required anymore in the case of a PCB that is multi-functional by nature, and where heat should be removed at specific locations, more precisely below the power semiconductor die only.